There is ample evidence suggesting that diets rich in fruit and vegetables protect against the development of chronic illnesses such as Coronary Heart Disease (CHD) and cancer, which are the major killer diseases among affluent populations. It has been recognized for some time that these beneficial effects are due, at least in part, to the antioxidant components of these foodstuffs, which can inhibit cellular damage by free radicals. In the body, free radical damage arises due to reactive oxygen species (ROS) being formed endogenously within the tissues, and also as a result of exposure to radicals arising from cigarette smoke, ionising radiation, air pollution and other environmental insults. These free radicals have the potential to interact with biological molecules such as proteins, lipids and DNA, and they are implicated in the aetiology of diverse diseases.
Antioxidants are likely to come into play in many aspects of multi-factorial disease conditions such as cancer or CHD, so it is difficult to establish how their primary effects are exerted. However, in the case of the process of atherogenesis a clear link has been demonstrated between oxidation of low density lipoprotein (LDL) and the formation of occlusive plaque in the arteries. Vitamin E (α-tocopherol) consumed as part of the diet is naturally present in the blood, where it acts to spare the LDL from oxidation. In vitro experiments have established that other natural sources of antioxidants, such as green tea, can also significantly retard the oxidation of LDL. In vivo studies have confirmed the in vitro tests, showing that increasing dietary intakes of some antioxidants, such as Vitamin E, can increase the resistance of LDL to oxidation and thereby reduce lesions in the arteries.
The main antioxidants from dietary sources are vitamins E (α-tocopherol) and C (ascorbic acid), the carotenoids, and polyphenols. Due to an increase in public awareness of the importance of these micronutrients, it has become commonplace for people to supplement their diets with natural or synthetic antioxidant sources. However, in spite of this general shift in favour of healthier eating patterns the incidence of CHD and cancer continues to be concerning.
It is clearly easier to encourage the use of dietary antioxidant supplements than to induce radical changes in the diet. But dietary supplements have their own drawbacks, particularly since there are detrimental side effects associated with high doses. Recently, for instance, the US Institute of Medicine advised that the upper limit of intake of vitamin E should be set at 1000 mg α-tocopherol per day, because of the risk of stroke and uncontrolled bleeding due to the anti-coagulant properties of this nutrient. β-carotene has actually been linked to an increase in the incidence of cancer. Thus, at the maximum safe dosage the antioxidant effect may be less than optimal.
Consequently, there is a need for new antioxidant products, which can be provided in the form of a food or as a dietary supplement, and which are potent in preventing CHD, cancer and other diseases associated with free radical generation, at dosages which do not pose health risks.